I know that adult is most often used to describe a mature human-being, and that mature is a broader usage word, describing everything form animals to cheese. Also that a young tree is a sapling....is there an equivalent word for a mature plant, tree or shrubbery? Or are we stuck with using mature/adult?

Is there a technical terms for when a plant has stopped growing in height, and is first able to produce fruit/flowers?

Actually, mature vines, for example, is probably the "standard" way of refering to them. And although it's relatively uncommon, adult vines turns up in Google Books at least a couple of hundred times.
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FumbleFingersDec 31 '11 at 14:35

@FumbleFingers: I know we say "mature wine", I'd never heard of "mature/adult vines". Seeing them now, I don't consider "mature vines" odd (probably because I associate "vines" with "wine"), but I wouldn't use "adult vines".
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IreneDec 31 '11 at 14:42

2

Looking at a few of the instances, it seems likely people with specialist familiarity tend to use adult vines as soon as they're 3-4 years old, whereas mature vines are more likely to be decades old.
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FumbleFingersDec 31 '11 at 14:58

I'm not sure if that's specific enough to what I'm describing. Ivy can be established, but that doesn't necessarily mean it's mature or adult, which seems to imply it's finished growing...
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PureferretDec 31 '11 at 16:27

The harvesting terms often refer to the fruits not the plant, and like wise the flowers on the flowering plant. There are several plants that stop growing (in size) but wait 1 or more years before flowering. So I'm not sure if this is what I'm after.
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PureferretDec 31 '11 at 19:33

Also, as an example, almost all carrots (that is, all except those used for seed production) are harvested during the year before they mature, maturity occurring after vernalization.
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jwpat7Jan 2 '12 at 2:27

Both you points are well taken; I just threw these in as alternatives, since I did not know the context. Having said that, though, couldn't vernalization be considered another alternative, at least for those plants which experience it?
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JeffSaholJan 2 '12 at 12:25